This disclosure relates to the sensing and reaction to open-circuits and shortcircuits. More specifically, the disclosure deals with a load network which is controlled by a central electronic controller or microprocessor. The circuit and method disclosed herein employs an input/output port from the electronic controller to send signals to the load network and to thereafter monitor the condition of the load network. The command signals are compared to the monitored condition; thereafter diagnostic and/or protection decisions can be implemented by the electronic controller.
In many complex automotive, information processing and robotic control systems, the outputs of a central electronic controller are connected to a network of motors, solenoids and other loads at various remote locations. The output devices within the controller are, obviously, vulnerable to damage by accidental short-circuits or opencircuits due to a variety causes.
To protect output transistors against short-circuits and open-circuits, shutdown circuits are often added to the system which monitor output current through a sensing resistor. This method adds significant cost and complexity to the output circuit, and increases the minimum voltage at which the circuit will satisfactorily drive the load.
In these systems, it is often highly desirable to have some level of "self-diagnostics". While the actuation of a shut-down circuit is a good indication of a shortcircuit, open-circuits are also likely. The ability to sense an open-circuit ranges in importance depending upon the application. Open-circuit indication can be used merely to simplify repair or, it may be used to initiate the use of redundant system elements so that operation may continue. Or, it may be used to shut the system down.
Open-circuit detection is sometimes accomplished by a current monitoring circuit which also uses a current-sensing resistor. Or, it may involve voltage sensing at the load. Again, these techniques may add significant cost and complexity to the system and may degrade its operation.
The technique to be presented here is a way to protect load drivers against shorted loads, and to detect both shorted and open loads at extremely low costs.